Tuning fork



Feb. 9, 1932. H. BROADWELL TUNING FORK Filed July 15 1929 Fla. 2

INVENTOH hi BROADWELL A 770/?NEV Patented Feb. 9, 1932 S ATES PAT -ENT orricsg HOWARD BRQADWE IQ VOFLVRID'GEWOOD, NEWJERSEY, AssIeNoa'ro BELL TELEPHONE LABORATORIES, "INCORPORATED, OF NEW YORK, N. Y., A ooRroaAmIoN or NEW "TUNING- FORK Application filed July 13,

"This invention relates in general to stroboscopic systems in whicha tuningforkis employed as a means for intermittentlyvmwmg a -rotating robject, i and more :particularly to 5 means for ac'tuating'the tuning fork tines.

limits- 'In this patent, a strobosco pe target is-emp'loyed upon which is impresseda plura'li ty of regularly disposed indications, the relative movements of which when viewed through a vibrating :tuning fork, indicate whether o'rnotthe dialis 'functioning at a speed desirable for the'proper operation of --automatic"telephoneswitches. In the system {disclosed by the patenteefa tuning fork is employed as a medium for intermittently or I successively viewing the rotating body, it

being necessary to strike th'e forktines'against Y of the mounting block 5 by meansof screws some stationary object or performing an equivalent operation, in orderto excite them and cause them to vibrate. It is apparent that-to firstexcite the fork and then 'focus it on the targetfintroduces an objection which is more pronounced whenthe time consumed -'by'ithe fork in vibrating'and the duration of the motion tobe studiedare relatively brief.

It 'is an ohjectof'thisi nvention to .permit the actuation of the tuning fork tines in a convenient manner, and while focused upon the object to'be stroboscopically studied.

I i This object is attained in accordance with a feature of the invention :by the provision of a finger. actuated mechanism associated withthettuning forktines which may be actuated (a slight pressure-of the finger of the tester tor-observer, :whilethe fork is being focused on the object.

' The invention will-be readily understood from the following detailed description made 1929. Serial Nb. 878,157.

nor :in which the cover isf slidably mounted on thebox; and,

Fig.5 is a fragmentary'view of the mounting block showing how the fork -is-secured thereto.

Referring to Figs. 2, Sand 5,:amounting block 5 is provided-with anextending portion having two bent in flan gesGfQrming azgroove into which the base or brldge portion-of the fork is staked. the fork comprising essentially' the tines 7 and 8.

Rotatably mounted on the'upper end of the mounting block 5, is aster-toothed wheelconstituting a ratchet 9.v .Acylindrical bearing portion 10 is located in juxtaposition with y :the ratchet9 and is mounted on the same shaft 2. r

Aspringpa-wl l1, securedcto the lower end 12,is provided with a circular hole through which the shaft :14 of the finger-button 13 is adapted to pass. The shaft l i'also passes through a-hole in the upper end ofmounting block (i-and is (prevented from being withdrawn therethroug'h by the lock nuts 15 whichare made up on the end of the shaft and abut against the mounting block when the button 13 is in its normal position. The

shaft 14 is provided with a collar 16 whichlimits its inward travel.

The mountingblock 5 also serves as a mounting for two spring members :17 and 18 which are secured thereto by means of'screws -60,'andare each provided with a projection 19 which normally rests. between two successive teeth on either side of the ratchet wheel.

Three tapped holes 20 are located on the mounting block as shown in Figs. 2 and 3 which accommodate screws21, by virtue of slightly which the tuning fork and its operating mechanism is secured within the box or casing 22. A hole in the side of the box permits the button 13 to protrude from the box as shown in Fig. 1.

The box 22 is provided with a cover 23 which is slidably secured to the box by means of an internally threaded cylindrical member 24 having a screw head secured at one end and adapted to receive the screw 25 at its other end. To position the cover, it is placed on the box-end and the member 24 passed through a circular hole in one side of the cover, then through two oppositely disposed oblong holes 33 in the upper end of the boX, and the screw 25 inserted in the hole 27 to engage and be threaded into the member 24. The upper end of thebox'is provided with oppositely disposed rectangular apertures 28 and 29 which align themselves with corresponding apertures such as 30 in the cover 23.

By virtue of the arrangement just described the tuning fork may be employed without completely removing the box cover. When not in use, the cover 23 is pushed down until-the cylindrical member 24 strikesthe bottom of the oblong holes 33. In this position of the cover the apertures effected by the rectangular openings 28 and 30 are closed. When in service, the cover 23 is raised until the cylindrical member 24 engages the upper extremities of the oblong holes 33. In this position, rectangular apertures are effected through which the flanged ends of the tuning fork tines may be observed. This arrangement serves as a shield and enables the observer to obtain a clear view of the stroboscope target without interference from objects which would otherwise be in the line of vision. 1 1 1 r V The operation of the device is effected in the following manner:

' The cover 23'is raised to the operating position and the box lifted so that the aperback edges of the ratchet teeth, they snap ture 35, effected by the rectangular openings 28' and 30, is in a line with the eye of the observer. It is understood that a corresponding aperture 35 is effected at the backof the device. The button 13 is then slightly depressed to effect an opening between the tuning fork tine ends as shown in Fig.3. The object to be studiedmay then be focused upon and viewed through the slit created by the distended fork tines. When the proper focus is obtained and with the device held conveniently to the observerseye, the button 13 is completely depressed. The inner end of button l3engages the working end of spring pawl 11-, forcing it inwardly. The pawl 11 is bent at an angle from the point at which-'t is engaged by the button 13 and terminates in an actuating tooth 36' and'a projection 37. The depressing of button 13 causes the tooth 36 to engage a tooth in the star-wheel 9, and the projection 37 to abut against and make sliding contact with the cylindrical portion 10 of the star-wheel 9. By this arrangement, and the peculiar formation of spring pawl 11 in general, the pawl is given sufficient stifl'ness to permit the tooth 36' to rotate the star-wheel one tooth, upon the actuation of button 13, and equally suflicient resiliency or flexibility to permit it to slide off the back of the next tooth upon the release ofthe button 13. g

The spring pawl 11, due to its irregular formation, is provided with the necessary rigidity to effect the movement of star-wheel 9 during its period of actuation, and also with sufficient resiliency to permit it to slidably disengage itself from the wheel and return to normal under its own action. This is a'very desirable characteristic in that it accomplishes an end which heretofore. in stepping mechanisms in general, was effected by a plurality of cooperating members. It is readily conceivable that this type of pawl is adaptable to any type of stepping mechanism, whether manually or electrically actuated, and is not specifically confined for its usefulness, to the tuning fork mechanism disclosed.

As the star-wheel 9 is advanced one tooth by'the pawl tooth 36, the projections 19 and 40 of spring members 18 and 17 .respectively, ride on the curved surfaces of oppositely disposed teeth in the star-wheel 9, and are forced outwardly and each into engagement with its associated tuning fork tine, the curved backs of the star-wheel teeth providing camming action. The upper end of spring 18 of which projection 19 is an integral part, engages the tine 7, whereas the upper end of spring 17 of which the projection 40 is an integral part, engages tine 8. As the projections 19 and 40 ride over the teeth in the star-wheel, due to therotation of the wheel, the springs 17 and 18, as well as the tines 8 and 7, are forced outwardly or distended.

As the projections 19 and 40 ride off the back into a position between adjacent teeth in the wheel under their own restoring force. The fork tines 7 and 8 are thereby suddenly released and caused to vibrate.

The rotating object to be studied may then be observed through the vibrating shutters or flanges 41 and 42 in the same manner as is shown and described in the above mentioned patent. In order to obtain the complete shielding effect of the box, it has been found advisable to hold the fork-box close to the object to be studied. Interference from external objects is thereby reduced to a minimum. A second advantage in holding the fork close to the object to be observed, is that the accuracy of the stroboscope readings, when the object speed is substantially the speed for which the stroboscope target is computed, is aided thereby, the inner edges of the tines acting as a reference by virtue of which very slow movement of the target divisions can be detected.

It is apparent from the foregoing description that applicant has devised a positive acting mechanism whereby the tines of a tuning fork may be set vibrating in a simple, convenient manner and while the fork is held focused on the object to be studied. This is I particularly desirable in instances where it is necessary for the tester or observer to manually actuate the rotatable body, such as a telephone dial. To actuate the fork tines of applicants invention requires but a slight pressure of the thumb and may be eflected while the fork is being focused with one hand and the object, such as a telephone dial, actuated with the other hand.

What is claimed is:

1. In combination, a tuning fork, a ratchet wheel, a pair of spring members interposed between the tines of said tuning fork having projections normally positioned between oppositely disposed pairs of teeth in said ratchet wheel and adapted to ride on the teeth of said Wheel upon its actuation to effect the dis tention and release of the tines of said tuning fork, to cause them to vibrate, and a finger actuated pawl for actuating said ratchet wheel.

2. In combination, a tuning fork, a mechanism for effecting the vibration of the tines of said tuning fork, a casing in which said fork and said mechanismare enclosed, said casing having oppositely disposed apertures, and a cover for said casing having apertures adapted to be aligned with the apertures in said casing when raised from its normal position to permit the tines of said fork to be observed Without removing the cover from the casing.

3. In combination, a tuning fork provided with a shutter on one end of each tine thereof, a mechanism for effecting the vibration of said tuning fork and'a housing for said fork and said mechanism comprising a sheath-like casing and a cover slidably secured thereto, said casing and cover being provided with cooperating means for effecting a sight slot through which the shutters on said fork tines may be observed only when the cover is raised from its normal position on the casing.

4. In combination, a tuning fork, a mecha nism for effecting the vibration of the tines of said tuning fork, a sheath-like casing entirely enclosing said tuning fork and said mechanism and a cover irremovably and slid- V ably secured to said casing, said casing and said cover having cooperating apertures adapted tocome into alignment to permit the tines of said fork to be observed when said cover is raised from its normal position.

In witness whereof, I hereunto subscribe my name this 12 day of July, 1929.

. HOWARD BROADWELL, 

